1. Field of the Invention
This invention relates to high frequency integrated circuit power amplifiers. More particularly, it relates to a push-pull power amplifier employing CMOS technology with capacitive neutralization in high resistivity silicon capable of operating linearly at frequencies in the gigahertz range.
2. Background Information
Bipolar transistors have been the successors to vacuum tubes in microwave amplification, until recently, when GaAs FET devices have received growing interest. Unfortunately, the GaAs FET exists only in N-type, precluding the circuit efficiencies attainable with complimentary devices. Silicon MOS devices are commonly available in CMOS, but with higher parasitic capacitance per transconductance than the GaAs devices. As a result, they have been ignored for high frequency applications.
Recently, a higher performance silicon technology has been developed in which the devices are formed in a thin active layer of silicon separated from high resistance silicon by an implanted insulating oxide layer. This configuration reduces the parasitic capacitance levels by an order of magnitude. Integrated circuits in accordance with this technology capable of operating in the gigahertz range are described in commonly owned U.S. patent application Ser. No. 07/583,059 filed Sep. 14, 1990 and entitled "Monolithic Microwave Integrated Circuit on High Resistivity Silicon".
Radio transmitters have long used push-pull vacuum tube power amplifiers with neutralizing capacitors to reduce the effects of parasitic capacitance, but they have also required inductive tuning. Such power amplifiers are very large and cannot operate in the gigahertz range.
There remains a need for a broadband integrated circuit power amplifier capable of operating in the gigahertz range.
There is a further need for such an integrated circuit power amplifier having high efficiency.
There is a related need for such an integrated circuit which can be implemented in CMOS technology in silicon.
There is also a need for such an integrated circuit power amplifier which can operate in the gigahertz range without the need for inductive tuning.